People who have attended art
classes have been taught that in order to produce depth in a painting
there must be a foreground, middle ground, and background. Control over
this dimension and depth usually is the result of planning and foresight.
As photographers we tend to often overlook the foreground and generally
allow the background to fall wherever it wants. Controlling the background
is an area of photography that can be mastered as long as the photographer
learns to think about what the scene will look like after appropriately
using a light meter to establish the true exposure of the subject.

Shifting The Key Of A Photograph
Changing the exposure or brightness of a primary subject area in order
to effectively raise or lower the exposure or brightness of the background
is a technique known as keyshifting, literally shifting the key of a photograph
higher or lower based on what happens to the primary subject.

The background exposure remains the same when we place a
diffused translucent panel between the sun and the subject,
decreasing the exposure on the subject without compensating
for the loss of light on the subject. Exposure remains at
1/250 sec at f/8.5.

If you've ever seen a movie
or video shoot, you've noticed the crew raising very large scrims of a
translucent material. The purpose is to allow light to travel through
the fabric in order to control the quality of light on the subject and
at the same time elevate the brightness of the background. The loss of
light caused by the fabric requires an adjustment of the exposure. Video
crews also use large lights bouncing into silver panels designed to brighten
the light on the subject in order to darken the brightness in the background.
By lighting the primary subject, background control is easy to achieve.

One of the easiest ways to
understand the effectiveness of keyshifting is to place a subject in bright
sunlight and make an exposure. The subject and the background will have
an equal brightness level. If you place a translucent material between
the subject and the sun, the subject will receive less light. By adjusting
the exposure for the loss of light on the subject, the background will
naturally get brighter.

As we open the aperture to correctly expose for the new
exposure on the subject, the background shifts brighter
by the same amount of light that the fabric decreased on
the subject. In this case, the exposure difference was 1
1/2 stops or f/5.6.

In terms of what the film sees,
taking light away from the subject effectively adds light to the background.
The more light you take away, the brighter the background will appear.
In this case, in addition to changing the background you are also changing
the quality of light on the subject. Diffusing the direct sunlight softens
the shadows and lowers the brightness of the highlights.

Understanding how to best use
this simple technique causes a photographer to look at backgrounds differently.
I will often look at a particular area that will be my background and
try to visualize what it will look like if it is overexposed by one or
sometimes even two stops. This will help me if I know I am going to place
a translucent disk or panel between my subject and the sun to change or
possibly improve the light quality on a face.

This photo was taken with an exposure on the subject of
f/11. The exposure of the background was also f/11.

Thinking Like Film
One of the first things photographers should try to understand is that
while metering for the brightness of any background in a studio or outdoors
in the park, the final exposure of a photograph will almost always be
based on the amount of brightness on the primary subject. This may or
may not be in the same light as the background. In many cases, they are
not in the same light. This means there are two options--to brighten or
darken the background. Either add light to the subject or take light away
from the subject.

A photographer who has full
control over his or her environment will take advantage of this technique
by previsualizing the scene and thinking about how it will appear on film,
not simply to the naked eye. Always keep in mind that our eyes will fool
us into seeing one thing while the film sees another.

In this image, I reduced the output of the main light on
the subject by one stop (f/8) and made the adjustment on
my lens aperture. This exposed my subject properly, yet
the background appears brighter.

Background Control In The
Studio
I learned how truly effective and important this lesson of control is
when working in the studio. When I wanted my background to be brighter,
I discovered that the background light was on its brightest or highest
power setting. Since I could not add light to my background to make it
brighter, I finally figured out that I could simply subtract light from
my subject. By then adjusting the exposure--opening up my lens aperture
to adjust for the loss on the subject--the background appeared to get
brighter. Again, the more light I take away, the brighter my background
appears.

The converse is also true.
If you need the background to be darker it's a problem if your background
light is on its lowest power setting. By thinking about shifting the key,
you can easily increase the brightness of the lights on your subject.
This will increase the subject brightness. When you close down your aperture
for the increase of light, your background gets darker.

By reducing the main light output by another stop (f/5.6)
and opening the aperture one stop to again keep the subject
properly exposed, the background shifts brighter, by another
full f/stop. The background was still receiving the same
amount of light as shown in the other two frames.

In applying this technique
to your own photography, try to remember it is as an exercise in thinking
more than anything else. It is all about thinking forward to the final
result and taking charge of your picture.

Tony L. Corbell is a long-time
professional photographer, educator, consultant, and author in the photographic
community. For more information, contact: www.corbellproductions.com.